<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
         .active{text-decoration:underline;}
        .text-danger{font-weight:blod;}
    </style>
</head>
<body>
    <div id="'app">

        <div v-bind:class="[isActive?'active':",'text-danger']">Hello School!</div>

    </div>
    
</body>
<script>
    var vm = new Vue({
        el:"#app",
        data:{
            isActive:true
        }
    })
</script>
</html>